1. Field of the Invention
This invention generally relates to water guns for producing in a body of water acoustic impulses which are useful, for example, for seismic exploration, and more particularly to such water guns that are operated exclusively by pneumatic means.
2. Description of the Prior Art
Generators for producing in water acoustic impulses are already known - see for example, U.S. Pat. Nos. 3,369,627, 3,642,090, 3,642,089, 3,711,824, 4,131,178, 4,185,714, 4,303,141 and French Pat. Nos. 2,307,999 and 2,308,112.
In U.S. Pat. No. 4,303,141 there is already described a liquid slug projector apparatus which comprises a generator having a housing whose bottom wall defines a main port adapted to be submerged in a liquid body for generating acoustic energy therein. The housing has a single bore forming a larger-diameter bore portion and a smaller-diameter bore portion. First and second shuttles are slidably mounted inside the generator's housing. The first shuttle forms with the housing a slug chamber for confining therein a liquid slug. The first shuttle is slidably mounted in the smaller-diameter bore portion, and the second shuttle is slidably mounted in the larger-diameter bore portion. Hydraulic and pneumatic means are operatively coupled to the generator's housing to cause the shuttles, during one complete cycle of operation, to move both separately from each other and in locked condition with each other. During each cycle, the first shuttle applies an abrupt propulsion force to the confined liquid slug which becomes expelled as a liquid jet through the main port in the bottom wall of the housing. The pneumatic means are adapted for (1) locking and maintaining the first and second shuttles in a rest position, (2) abruptly releasing the first shuttle from the second shuttle, and (3) propelling the first shuttle toward the main port in the housing's bottom wall, thereby expelling the liquid slug into the outside liquid body. The hydraulic means are adapted for moving the second shuttle toward the first shuttle. Thereafter, the pneumatic means return the thusly locked first and second shuttles to their initial or rest position, thereby completing a full cycle of operation.
It is a main object of the present invention to provide an acoustic generator which can be operated entirely pneumatically.